The present invention relates generally to rotating electric machinery and, more particularly, to a method and system for improving voltage regulator accuracy in vehicle alternators.
Generators are found in virtually every motor vehicle manufactured today. These generators, also referred to as alternators, produce electricity necessary to power a vehicle's electrical accessories, as well as to charge a vehicle's battery. Generators must also provide the capability to produce electricity in sufficient quantities so to power a vehicle's electrical system in a manner that is compatible with the vehicle's electrical components. The alternator or generator typically uses a voltage regulator to regulate the charging voltage and output current in order to provide consistent operation during varying loads that would otherwise create voltage drops and other operational problems. Presently, conventional vehicle charging systems may utilize a voltage regulator having either a discrete transistor or, alternatively, a custom integrated circuit known as an Application Specific Integrated Circuit (ASIC).
Still other vehicle designs may also employ voltage regulators with advanced microprocessor functions that maintain a highly accurate regulated voltage produced by a generator. Microprocessor based regulators may also include advanced clock and memory circuits that store battery and power supply reference data, battery voltage and generator rotation speed, as well determine how much the battery is being charged and at what rate at any point in time.
As such advanced voltage regulator systems can be expensive, it would be desirable to be able to improve the accuracy and resolution of existing (and lesser expensive) microprocessor based regulator devices. For example, the resolution of one type of microprocessor based voltage regulator employing a 10-bit analog-to-digital converter is (for measuring a 20 volt range signal in a 12 volt alternator system) about 0.02 volts. That is, the microprocessor is only able to read an input voltage in 20 mV increments. On the other hand, the resolution of a pulse width modulation (PWM) driver used to control the duty cycle of the field current (between 0% and 100%) is about 500 steps (i.e., 0.2% increments). In terms of a set point system voltage (e.g., 14 volts), a conventional linear based regulation technique utilizes PWM steps when the system voltage is both above and below the set point. Thus, the actual accuracy of the regulated voltage does not match the resolution of the detectable voltage (i.e., +/−20 mV).
Accordingly, it would be desirable to be able to increase the accuracy of microprocessor based voltage regulators in a manner that avoids the addition of costly components that increase the resolution of the voltage detection capability (e.g., through a differential amplifier or microprocessor with 12-bit ADC capability.